1. Field of Invention
This invention relates to an injection nozzle and piston designed for use in a compression ignition (diesel) internal combustion engine.
2. Description of Related Art
Internal combustion engine designers continue to confront an ever more demanding set of governmentally mandated emissions standards and performance objectives. Modifications made to meet one standard or improve engine performance may lead to increased emissions of a type that cause another standard to be exceeded. Thus, designers are often confronted with not only the challenge of meeting a desired performance objective or a newly imposed emission standard but to do so in a way that does not cause other emissions standards, previously met or newly imposed, to be exceeded.
An example of the difficulties created for engine designers is that created by a new set of diesel engine standards, known as TALuft, that have been promulgated for application in the European market. These standards require the diesel engine to operate below the following limits at all engine operating points based upon a fuel consumption greater than 552 pounds per hour:
NO.sub.x 2 grams/M.sup.3 PA1 Carbon Monoxide 650 mg/M.sup.3 PA1 Unburnt Hydrocarbon (HC) 150 mg/M.sup.3 PA1 Particulate 130 mg/M.sup.3 PA1 A. the ratio of BD/CD is greater than or equal to 0.54 and is less than or equal to 0.75, PA1 B. the ratio of BD/L is greater than 6.2 and is less than or equal to 7.0, PA1 C. wherein the ratio of BD/R, is greater than or equal to 1.3 and is less than or equal to 3.4, or PA1 D. the ratio of R.sub.2 /R.sub.1 is greater than 0.14 and is less than or equal to 0.32. PA1 A. the ratio of BD/CD is greater than or equal to 0.54 and is less than or equal to 0.75, and is preferably 0.70; PA1 B. the ratio of BD/L is greater than 6.2 and is less than or equal to 7.0, and is preferably 6.67; PA1 C. wherein the ratio of BD/R.sub.1 is greater than or equal to 1.3 and is less than or equal to 3.4, and is preferably 1.42; and PA1 D. the ratio of R.sub.2 /R.sub.1 is greater than 0.14 and is less than or equal to 0.32, and is preferably 0.152.
These levels are for 5% dry oxygen in exhaust
Changes in any one of a variety of engine design variables or engine operating variables such as engine compression; combustion chamber shape; rate and location of combustion chamber cooling and/or fuel injection spray pattern, pressure, timing and/or flow rate can have an effect on the emissions in one or more of the above categories. However, such changes can often cause emission in another category to exceed the acceptable limit. For example, as the brake mean effective pressure (bmep) is desirably increased, a tendency arises for smoke in the engine's exhaust to increase. This problem is accentuated by the need to achieve other critical engine operating characteristics such as fuel economy, high torque output, low operating costs and/or reduced maintenance. As one example, the amount of soot that is entrained in the engine's lubrication oil can have a profound effect on the cost of operation and the length of service before a major overhaul is required. Soot is very abrasive and can cause high wear if allowed to become entrained in the engine's lubrication oil to any substantial degree. The amount of soot entrained in the engine's exhaust can be effected by a number of factors such as combustion chamber shape and fuel injection spray angle but changes in these variables can have the undesired effect of actually increasing the other emissions such as smoke and CO emissions entrained in the engines's exhaust.
Many attempts have been made to produce an ideal flow pattern for the charge air and fuel within the combustion chamber of an internal combustion chamber. For example, provision of a combustion bowl in the upper region of a piston to cause, among other things, fuel/charge air mixture within a direct injection engine is well known as disclosed the article entitled "Future Developments . . . ", Automotive Industries, Oct. 15, 1952. While most of the combustion bowl designs disclosed in this article appear to be symmetric about a central axis, the article does not address the critical relationship of the combustion bowl shape and the fuel injection pattern on the specific problems addressed by the subject invention.
A variety of piston designs have been disclosed including symmetrical bowl shaped recesses formed in the upper surface of the piston crown to achieve desired flow patterns within the combustion chamber formed in part by the piston. For example, U.S Pat. No. 4,377,967 discloses an articulated piston assembly including a crown containing a symmetrical combustion bowl in the top surface defined by a cone shaped central floor section which connects at its base to an arcuate surface of revolution coaxial with the central axis of the cone surface wherein the surface of revolution flares upwardly to join with the uppermost surface of the piston. The base of the cone shaped central floor section extends over no more than approximately, 50% of the diameter of the bowl.
The following patents disclose piston designs including cavities in the upper section of the pistons which appear to be symmetrical about a central axis and have a central raised floor section extending radially for a substantial portion of the diameter of the combustion bowl wherein the raised floor section has a relatively large radius of curvature in diametric cross-section and wherein the outer portion of the bowl is characterized by a surface of revolution coaxial with the raised floor section and shaped to form an upwardly curved outer sidewall of the cavity: U.K Patnt Application No. 2,075,147 published Nov. 11, 1996 (FIGS. 1 and 2); U.S. Patent No. 5,029,563 issued Jul. 9, 1996 (FIG. 4) and U.S. Pat. No. 3,508,531 issued Apr. 28, 1970 (FIG. 2). In diametric cross section the curved sidewall, in each instance, would appear to have a radius of curvature that is substantially less than the radius of curvature of the central raised floor section. None of these references discloses any critical size ratios for the disclosed combustion bowl designs and none discloses the importance of the angle of the spray orifices in relationship to the combustion bowl shape.
The assignee of the subject invention, Cummins Engine Company, Inc., is also the assignee of previously issued patents disclosing diesel engine piston designs which incorporate combustion bowl designs. For example, U.S. Pat. No. 1,865,841 issued Jul. 5, 1932 and U.S. Pat. No. 4,242,948 issued Jan. 6, 1981 disclose pistons having a combustion bowl with a "Mexican-hat" design but both of these patents fails to disclose that the combustion bowl has crucial dimensional relationships that are required to achieve specific engine functionalities.
The Cummins Engine Company, Inc. has used commercially articulated pistons having a symmetrical bowl formed in the upper surface of the piston crown but wherein the base of the cone shaped center section extends over a substantial portion of the diameter of the bowl and the apex of the cone is truncated to form a frusto-conical surface.
Many other piston designs containing symmetric combustion bowl designs have been disclosed in previously issued patents. Note, for example, the following patents:
______________________________________ U.S. Pat. Nos. 3,805,677 4,662,319 4,056,044 4,781,159 4,161,165 4,909,132 4,180,027 4,989,559 4,286,505 5,040,454 Foreign Patents European Patent No. 0,071,994 Feb. 16, 1983 German Patent No. 1,301,657 Aug. 21, 1969 Japanese App. No. 59-155551 Sept. 4, 1984 German (East) Patent No. 1588 06 Feb. 2, 1983 Russian App. No. SU 1107870 A Aug. 15, 1984 Japanese App. No. 60-135651 July 19, 1985 U.K. App. No. 2,079,851 Jan. 27, 1982 ______________________________________
Other prior art piston designs have been disclosed with combustion bowls having specialized shapes designed for producing a desired effect within the combustion chamber. For example the following patents disclose pistons with asymmetrical shapes:
______________________________________ U.S. Pat. Nos. 2,709,992 5,305,720 3,020,900 5,320,075 4,759,323 5,322,042 5,020,485 Foreign Patents U.K. Pat. Spec. No. 465,656 May 10, 1937 U.K. Pat. Spec. No. 713,637 Aug. 18, 1950 German Patent Doc. No. M17120 Ia//46a Aug. 30, 1996 French Patent No. 1,217,467 Dec. 7, 1959 ______________________________________
Despite the many examples of piston designs including combustion bowls in the upper portion of the piston contained in the prior art, none has disclosed a design that is said to function cooperatively with an injector spray plume in a manner to minimize soot entrainment in the engine lubrication oil and simultaneously maintains acceptably low exhaust emissions. A need, thus, exists for a piston and complementary injector design that is capable of achieving this combination of functionality.